The present invention relates to a device for detecting pressure fluctuations in a combustion chamber of an internal combustion engine by means of at least one transmitter receiving ionic current produced by ionized gases in the combustion chamber.
It has been known that pressure fluctuations in the combustion chamber of the internal combustion engine are detected by ionic current probes. It is the fact of practice that during the combustion of hydrocarbonous materials, electrically charged molecules and atoms, that is ions and free electrons occur. If a measuring voltage is applied to the arrangement with two electrodes positioned in the combustion chamber an ionic current is produced which depends upon an ion concentration. This ionic current is measured and its value is the value of the combustion process that takes place in the combustion chamber. It is known that an ionic current signal is used for detecting a knocking in the internal combustion engine. However, for detecting that knocking, complicated evaluation circuits have been required. The knocking effect in the combustion chamber means wave-like vibrations of the gas mixture occuring in the combustion chamber of the internal combustion engine during combustion. These vibrations are caused by an accelerating chemical reaction of the non-burned air/fuel mixture in the end gas region of the combustion chamber and lead to the occurrence of the knocking per time unit. Since a strong thermal loading usually takes place inside the combustion chamber upon the occurrence of knocking and a material wear off can occur, efforts should be made to avoid or substantially reduce the knocking. If knocking occurs for a long period of time this could lead to damaging of the internal combustion engine. Therefore the occurrence of knocking must be discovered in the internal combustion chamber as soon as possible.